The present invention relates to conical, unimpregnated windings for use in superconducting magnets.
Superconducting magnets allow for very high current densities in the magnet windings, enabling generation of very high magnetic fields, about 10 times the field generated by the most powerful resistive air core magnets. Since superconductors exhibit the property of carrying electrical current resistance free only at cryogenic temperatures, the magnets have to be cryocooled by liquid helium and nitrogen.
Epoxy-impregnated windings have proven, predictable performance in superconducting magnetic resonance magnets. The windings typically require an ultraclean, precision winding, complex epoxy-impregnation process, precision machining, and assembly to the cylindrical support structure. If the epoxy-impregnation of the wires and assembly to the support structure are not properly done, then, when the epoxy-impregnated windings and support are placed inside a cryostat and cryocooled by liquid helium, cracks between the support and epoxy-impregnated windings can occur due to the differential cooling rates of the form and the windings. Electromagnetic forces, due to the current flowing in the windings, exert outward forces on the windings. Any resulting movement of the windings can cause heating of the windings, raising a portion of the windings above the superconducting temperature, resulting in resistance heating of the winding. Resistance heating of a portion of the winding can further heat adjacent areas, resulting in a quench of loss of superconductivity of the current-carrying winding. The heat released from the winding can result in rapid evaporation of liquid helium from the cryostat.
Training is presently used to solve the wire movement problem in defective magnets. During training of the magnet, the magnet is supercooled and current flow is increased toward rated power. Wire movement occurs and a quench results. The magnet is again cooled and current levels increased in the hope and expectation that the windings that previously moved and caused the quench will stay in their new position. Training is a time-consuming, expensive (due to lost helium) and not always an effective fix.
There are limited degrees of freedom, to optimize the winding geometry of an epoxy-impregnated magnet, for reducing the peak field of the windings and, therefore, the stress that the windings are subjected to. This constraint results from the requirement to limit the coil axial length to help ensure void-free epoxy impregnation. Consequently, utilization of the epoxy-impregnated windings is less than optimum.
It is an object of the present invention to provide a non-impregnated winding for a superconducting magnet which can perform predictably without training.
It is another object of the present invention to provide a non-impregnated winding for superconducting magnets that is simple to manufacture and design to improve superconductor utilization and reduce cost.
It is still another object of the present invention to utilize the winding support structure to protect the winding during a quench and, thereby, eliminate magnet protection resistors.